Since the Congressional Budget Office (CBO) released its analysis of the House-passed health-care bill just before Memorial Day, conservatives have questioned CBO’s assumptions on several fronts—most notably scorekeepers’ almost dogmatic belief that an individual mandate holds the key to enticing tens of millions of Americans to purchase health coverage. But the CBO report revealed another key issue—the budget office’s inherent bias towards liberal cost-saving solutions rather than conservative ones.

That bias stems from one conclusion: Under the bill, a “few million people [CBO didn’t provide a more specific number] would buy policies that would not cover major medical risk.” In these cases, “the policies [purchased] would not provide sufficient financial protection to meet CBO’s definition of insurance coverage,” and “would not provide enough financial protection in the event of a serious and costly illness to be considered insurance.”

At first glance, it seems reasonable for CBO to, when analyzing legislation, determine whether individuals scored as having “insurance” actually possess coverage meeting that definition. However, that position looks more questionable when the budget office acknowledged in a December blog post the administrative and other difficulties in arriving at a uniform definition of private health insurance, which the office did not quantify—either in December or in its score of the House bill.

More importantly, though, at no point has CBO attempted to quantify whether and to what extent Americans—particularly those in government programs—are under-insured due to their inability to obtain medical treatment. Largely due to poor reimbursement levels for physicians and hospitals, some participants in programs like Medicaid may have great financial protection in theory, but little access to care in practice.

Conservative Versus Liberal Goals For Health Care

At the risk of stereotyping, conservatives often prefer less-comprehensive insurance—coverage largely for catastrophic expenses, with patients paying for many routine expenses out-of-pocket. Right-leaning analysts believe that by making costs explicit to patients—to use the wonky phrase, giving patients “skin in the game”—they will make smarter health care choices. By contrast, liberals generally make costs and tradeoffs opaque, supporting generous coverage of most medical procedures, while reducing costs to government through lower provider reimbursement levels often not visible to patients.

Obamacare provides an excellent example of the contrast. Two months after the law passed—while attempting to deflect the criticism that Democrats took money from Medicare to pay for Obamacare—Nancy Pelosi noted that the law included “no change in guaranteed benefits.”

But in reality, the vaunted “Medicare guarantee” that Pelosi and liberals purport to defend doesn’t exist. The law guarantees that the federal government will pay seniors’ doctors and hospitals for treating them, but it doesn’t guarantee that seniors will actually get seen by a doctor.

In government programs, low reimbursement levels can make treatment hard for patients to obtain. At a briefing on “under-insurance” several years ago, an official who used to run one state’s Medicaid program acknowledged the access problem in government programs, admitting that “a Medicaid card [is] a hunting license…a chance to go try to find a doctor.”

Obamacare Made A Bad Situation Worse

On provider reimbursement, Obamacare made a bad situation worse. The nonpartisan Medicare actuary considers a series of payment reductions included in the law so Draconian—by 2040, half of all hospitals, and 90 percent of home health agencies, would be unprofitable—that they will not go into effect, “to ensure Medicare beneficiaries continue to have access to health care services.”

CBO has acknowledged the limitations on access created by Obamacare. In 2014, it noted that the new Exchange plans created that year had lower physician reimbursement levels and narrower provider networks than most employer plans. It has also estimated last fall that, thanks to the Medicare payment reductions included in Obamacare, up to half of all hospitals nationwide could be operating in the red by 2025—which could harm access to care, not just for seniors but all Americans.

However, CBO has not attempted to quantify the effects of these reimbursement reductions on the end-users—patients. It seems somehow perverse that a state Medicaid program could reduce payment levels to such absurdly low levels (99 cents, perhaps?) that no doctor or hospital would treat those patients, yet these individuals would continue to be classified as “insured” by the budget office, while those whose private coverage exceeds CBO’s not-publicly-defined thresholds for “acceptable” insurance would not be.

Some critiques of CBO’s work on the House health care bill appear opportunistic. Protesting that many fewer Americans than CBO projects will drop coverage upon repeal of the individual mandate, without acknowledging that such a scenario would likely obliterate the budgetary savings in the House legislation, seems incongruous at best. But a budget office that examines only one side of the “under-insured” coin—Americans who face high out-of-pocket costs, but not those who cannot access care—likewise seems out of whack. Republicans in Congress should press CBO to quantify both sides of this important health-care issue.

Mr. Jacobs is founder and CEO of Juniper Research Group, and author of the forthcoming book, "The Case Against Single Payer." He is on Twitter: @chrisjacobsHC.